Hiroshima mayor calls on Japan to serve as a bridge

The anniversary came after Japan sided last month with nuclear powers Britain, France and the United States to dismiss a United Nations treaty banning atomic weapons, which was rejected by critics for ignoring the reality of security threats such as North Korea.

The U.N. estimates nations around the world still have some 15,000 nuclear weapons in their arsenals.

Several thousand people - including Prime Minister Shinzo Abe and survivors - observed a minute's silence in the center of the western Japanese city in memory of the victims at 8:15 am (UTC 2315), the time when a US B-29 bomber dropped the first atomic bomb on the city on August 6, 1945.

Japan is the only country to have suffered atomic attacks.

Guterres urged United Nations member states to intensify their efforts in the shared pursuit of a nuclear-weapons-free world.

"For us to truly realise a "world without nuclear weapons", the participation of both nuclear weapon states and non-nuclear weapon states is necessary", he said.

The anniversary comes amid growing concern in Japan over North Korea's recent missile tests, and mounting tension over its nuclear programme.

Hiroshima Mayor Kazumi Matsui on this occasion urged that the absolute evil of atomic weaponry be banished. You could find yourself suffering their cruelty.

"Given this development, the governments of all countries must now strive to advance further toward a nuclear-weapon-free world", Matsui said in his annual Peace Declaration.

"The states possessing nuclear weapons have special responsibility to undertake concrete and irreversible steps on nuclear disarmament", Guterres stressed.